Recently, along with the spread of digital cameras or such, it becomes possible to obtain images superior in image quality thanks to digital image processing. For example, in a photographing apparatus such as a digital camera, a correction process such as an image stabilizer function or a noise removal function is mounted, and thus, image quality of an image taken through photographing by the photographing apparatus has been improved.
As a method of image stabilization, there is a method of optically carrying out image stabilization and a method of carrying out image stabilization by image processing. The former method is such that blurring is corrected mechanically, an optical system is moved, and thus, image stabilization is achieved. This method is used for an apparatus having a mounting space for mounting related mechanisms. In contrast thereto, the later method is such that image stabilization is achieved by image processing. Therefore, this method is suitable for an apparatus for which a mounting space is limited.
For example, in a digital camera or a cellular phone with a camera function, images continuously taken with a short exposure time are synthesized (superposed). Influence of blurring associated with a motion of the camera or such is small in the images thus taken with the short exposure time. However, in these images, the amount of light is small. Therefore, the images obtained through continuous shooting are synthesized, and an image having reduced noise and controlled blurring associated with the motion of the camera or such is generated.
FIGS. 1A, 1B and 1C illustrate the related art. FIG. 1A depicts an image such that since an exposure time is long, a blur amount is large, and consequently, the image is blurred. FIG. 1B depicts images taken through continuous shooting with a short exposure time. These images have been taken with the short exposure time, and thus, a blurring amount is small. However, since a sufficient amount of light may not be obtained, the images are dark.
FIG. 1C depicts an image obtained from superposing the images of FIG. 1B. It is possible to compensate insufficiency of the amount of light by superposing the plurality of images.
In this technique of image stabilization by image processing, basic processes include a position adjustment process and a superposition process to be carried out on purl images. When the position adjustment process is not properly carried out, image degradation such that an image obtained from the superposition process may look as if it is blurred, or such.
One reason why the position adjustment process is not properly carried out can be, for example, as follows. Since position adjustment is carried out basically by using parallel translation in many cases, it may not be possible to properly carry out position adjustment on images taken with a motion of the camera including rotation. The reason why parallel translation is basically used to carry out position adjustment is that it is possible to reduce a data processing load in comparison to a case of carrying out a rotation process.
Therefore, in order to obtain a satisfactory synthesized image, for example, a position change is obtained from a signal output of a photographing device during exposure, image stabilization is carried out as a result of images being synthesized based on the position change, and image data of an image area that has not been synthesized is corrected (see Japanese Laid-Open Patent Application No. 2005-101837 (Patent Document 1)).
Further, a relative displacement between two images of an associated plurality of images is obtained, images having low reliability in the relative displacement are not used for a superposition process, images having high reliability in the relative displacement are synthesized, and thus, proper image stabilization is carried out (see Japanese Laid-Open Patent Application 2007-272459 (Patent Document 2)).